1. Field of Invention
Various exemplary embodiments of the present invention relate to a semiconductor device, and more particularly, to a 3-dimensional (3D) semiconductor memory device.
2. Description of Related Art
A 3D semiconductor memory device is proposed as a way to overcome the integration limit of 2D semiconductor memory devices.
Cell strings of a 2D semiconductor memory device are planarly arranged on a semiconductor substrate, and cell strings of a 3D semiconductor memory device are vertically arranged on a semiconductor substrate. As the size of memory cells in the 2D semiconductor memory device shrink, interference and disturbance increase, and it is difficult to perform operations such as a multi-level cell (MLC) operation in a 2-dimensional semiconductor memory device. On the contrary, in 3-dimensional semiconductor memory devices, the area of the semiconductor substrate can be efficiently used because it incorporates a stacked structure perpendicular to the semiconductor substrate. Therefore, it is easier to improve the integration degree in 3D semiconductor memory devices than in 2D semiconductor memory devices, and recently, various technologies for increasing integration have been proposed.